A STN (super twist nematic) mode, a TFT mode and an IPS mode have been used in liquid crystal display elements for large-sized displays useful in notebook-type personal computers and word processors etc. Polyimide type materials having various constitutions have been proposed as aligning films useful for them (Japanese Patent Application Laid-open Nos. 61-205924 and 62-297819).
However, superior characteristics have been required increasingly heretofore as to liquid crystal aligning films with recent improvements in characteristics of liquid crystal displays.
Liquid crystal aligning films have been hitherto required to have superior electro-optic characteristics such as good aligning property and high voltage holding ratio etc., and in recent years fine Vth unevenness formed with in a display plane has become an issue, as liquid crystals having high dielectric anisotropy have been used for lowering of crystal driving voltage. In particular, there occurs phenomenon that water washed traces remain as Vth unevenness when water washing being carried out in order to remove dust formed during rubbing of aligning films, so that, conventional liquid crystal aligning films cannot been said sufficient for decreasing the phenomenon.
As an example of aligning films from which high quality liquid crystal display elements being obtained, there has been proposed a polyimide aligning film which is obtained from 4,4'-diaminodiphenyl methane and cyclobutane tetracarboxylic dianhydride in Japanese Patent Publication No. 4-33010. The main component of the film is polyimide resin in which at least 90 mol % of repeated units in polyimide being constituting units expressed by formula ##STR1## wherein R denotes divalent aromatic hydrocarbon radical, and the film is superior in its transparency and heat resistance. Therein, 4,4'-diaminodiphenyl methane is said to be effective as diamine.
Further, in Japanese Patent Application Laid-open No. 4-57027, it was disclosed that by using polyimide with poly-condensed structure of a cyclobutane tetracarboxylic dianhydride component and a 4,4'-diaminodiphenyl methane component as an aligning film, the film has a high voltage holding ratio and is suitable for an active matrix type liquid crystal display device.
However, in the case that a substrate of liquid crystal display element is washed with water in order to remove impurities adhered on a surface of an aligning film during preparation of the liquid crystal element, there is a problem that faint washing traces remain at the time of lightening the entire screen of the said liquid crystal display element in intermediate tone. In particular, washing traces remain clear in the case that liquid crystals with high dielectric constant being used.
A problem to be solved by the invention is to propose a composition for a liquid crystal aligning film having characteristics hitherto required for an aligning film, such as good aligning property, high voltage holding property and no water washing unevenness when water washing being carried out; a liquid crystal aligning film formed therefrom; as well as a liquid crystal displays and a liquid crystal display element with use of them.